The present invention relates to a multiplex transmission system for a vehicle, wherein; a multiplex transmission method such as a CSMA/CD is employed to transmit signals in a vehicle. More particularly, the present invention relates to an improvement in how to quickly report a failure that has taken place in a communication node to other nodes.
A critical problem arises in that an enlargement of the wiring (wire harness) for connecting electronic parts to one another and complexity of the same become excessive in accordance with the recent advancement of electronic technology in vehicles. In order to particularly overcome a problem of the type described above in the field of the vehicles, a multiplex communication has been attracting attention. The multiplex communication is a system of transmitting a plurality of data items through one wire in a time division manner generally in accordance with a serial transmission method.
In the field of multiplex communication of vehicles, the types of network can be classified into a complete multiplex type and a partially multiplex type or classified into a centralized type and a decentralized type. The partially multiplex type has a structure formed by mixing non-multiplex communication portions and multiplex communication portions. The above-described multiplex communication portions are arranged in a manner that such switches and loads which are disposed away from one another are connected by multiplex communication units. Since the unit and the switches must be independently connected to one another by a wire and the unit and the loads must also be independently connected to one another by another wire, the overall length of wires can be shortened. However, the number of wires is undesirably increased. The centralized type network is arranged in such a manner that a plurality of slave transmission units are connected to one master transmission unit. Therefore, although an effect of reducing the bulk volume of the transmission lines can be obtained, the overall system will break down if the master transmission unit breaks down. Furthermore, another problem arises in that the design cannot easily be changed. On the other hand, the decentralized type network attracts attention (disclosed in, for example, Japanese Patent Laid-Open No. 62-4658) in spite of its high cost because the decentralized type network has a significant effect of reducing the bulk volume of the transmission lines, an excellent reliability against a breakdown and satisfactory flexibility in design change.
The decentralized multiplex communication system is arranged to employ the CSMA/CD method according to a SAE (Society of Automotive Engineers) standard design. In Japanese Patent Publication No. 62-302421 (which corresponds to U.S. Pat. No. 4,951,281 commonly assigned to the assignee of the present invention, there is disclosed a PALMNET (Protocol for Automobile Local Area Network), which is an improvement of the above-described CSMA/CD method. Furthermore, according to a disclosure made by the assignee of the present invention in Japanese Patent Laid-Open No. 64-36541, a master node is provided to transmit reference pulses for time-dividing bus access rights so as to provide channels on a transmission passage.
In the conventional decentralized multiplex communication system for use in a vehicle, a critical problem does not rise in the data communicating speed since simply structured switches or solenoids are adopted to this system. However, if an engine controller, an active suspension controller, a traction controller and the like are intended to be adopted to the multiplex communication, a problem of communicating speed a rises since the above-described controllers respectively need a large quantity of information items to be processed. It is an essential factor for the decentralized multiplex communication system for use in a vehicle and consisting of nodes which have the controllers needing the high speed data process to quickly detect the state of a failure taken place in a node. If the failure is detected after a time delay, the control of the overall system is undesirably performed in accordance with incorrect or old data.
Hitherto, the node which has detected its failure transmits a frame indicating the occurrence of the failure to the network so as to report it to the overall system. An example of a structure in which the frame showing the occurrence of a failure is transmitted has been disclosed in U.S. Pat. No. 5,090,012 by the assignee of the present invention. However, the decentralized multiplex transmission system for use in a vehicle creates a problem in that a failure report cannot sometimes be performed quickly because an access right for the transmission passage is necessary to report the failure state to the system.